1. Field of the Invention
This invention relates to an apparatus and method providing hyperthermia treatment of living tissue and more particularly to an accurate measurement and control of the temperature of the living tissue during hyperthermia treatment.
2. Description of the Prior Art
When a patient has a cancerous tumor, a surgical procedure is often employed to remove the tumor. However, in certain circumstances the use of surgical procedures may not be advisable.
Since ancient times, medical practitioners have known that the patient may be successfully treated by raising the temperature of a tumor, a treatment generally referred to as hyperthermia. One method of hyperthermia is the elevation of the temperature of a large portion of the patient's body where the tumor is located. Accordingly, in the late 1960's, medical practitioners treated patients with tumors in their arms and legs by a perfusion therethrough of hot blood. In another method, patients with tumors in their bladders were treated by flushing the bladders with hot fluid. In 1974 Scottish medical practitioners immersed patients in hot wax. Other medical practitioners have elevated the body temperature of patients by infecting the patients with malaria.
It is known that certain tumors either shrink or disappear at a temperature of approximately 43.degree. C. Based on this knowledge, one preferred method of hyperthermia tumor treatment provides for heating the tumor to that temperature by heating only so much of the tissue as includes the tumor. Medical practitioners have used microwave radiation energy to elevate the temperature of the so-called "local tissue" which is contiguous and closely adjacent to the tumor. Depth of penetration of the energy signal into the tissue of the body is a well-known and well-behaved function of the signal frequency employed. The temperature of the tissue is directly dependent on the power or intensity of the microwave energy applied to the surface of the body tissue. The volume of the tissue to be heated can be controlled by the electrical and geometric design of the microwave applicator. The microwave radiation may be controlled to elevate rapidly the temperature of a known volume of tissue that extends from the surface of the skin to a known depth beneath the skin. During microwave radiation, it is desirable to prevent over-heating of the tumor as well as surrounding living tissue. Therefore, it is correspondingly desirable to provide an accurate measurement of the temperature of the living tissue particularly at the site of the tumor. Prior methods of hyperthermia treatment employed thermocouples to measure the temperature of the tissue. Thermocouples are either attached to the surface of the skin or invasively positioned beneath the skin. The thermocouple while measuring temperature during treatment can be used to switch-off the microwave irradiation to the tissue upon sensing a predetermined temperature. However, thermocouples can only measure the temperature of the tissue at the point of contact. Thus, thermocouples for hyperthermia treatment are located at the skin surface or subcutaneously by being positioned invasively at the site of the tumor, requiring thereby surgical insertion of the thermocouple. Also, thermocouples, being metallic, distort the applied microwave field and induce extraneous heating effects which contribute to inaccurate temperature measurements. Furthermore, thermocouples behave as radiation detectors and therefore are susceptible to pick-up signals of radiated frequencies other than from the applied microwave source, whereby inaccurate temperature readings may occur. It appears, thus, that the use of thermocouples for measurement of temperature does not provide the accuracy required for improving the results of hyperthermia treatments.
It is also known to use radiometers to sense subcutaneous temperatures for diagnosing malignant tumors. For further information of this technique see an article in Science, Nov. 14 1975, Volume 190, pages 669-671, by Barrett and Meyers entitled "Subcutaneous Temperature: A Method of Noninvasive Sensing." Also see an article in The Review of Scientific Instruments, July 1946, Vol. 17, No. 7, pages 268-275, by R. H. Dicke, entitled "The Measurement of Thermal Radiation at Microwave Frequencies."
There is a need in hyperthermia treatment of living tissue, whether or not tumors are included therein, to provide an accurate measurement of the volume of the heated tissue to minimize if not eliminate the risk to the patient for successful hyperthermia treatment.